This NIH Ischemic SCOR will devote itself during its second year of activity to continuing the development and refinement of new means of identifying, localizing and sizing myocardial infarcts in experimental animals and in patients. In addition, considerable effort will be devoted to identifying the role of cell swelling, lysosomal changes, and other pathophysiological alterations occrring during myocardial ischemia that might be responsible for perpetuating the ischemic process. The latter studies will be performed with the expectation that from a better understanding of the pathophysiological processes occurring in myocardial ischemia might come certain physiological or pharmacological interventions that would effectively limit infarct size in experimental animals and in man. The major accomplishments of our Ischemic SCOR activities are: 1) the further development and utilization of technetium-99m stannous pyrophosphate (99mTc-PYP) myocardial scintigrams to identify the presence of, localize and size acute myocardial infarcts in experimental animals and in man, 2) the development of "combined myocardial imaging" using both thallium-201 (201T1) and 99mTc-PYP in order to identify and size old and new areas of myocardial damage in experimental animals and in man, 3) a precise understanding of the pathophysiology involved in the development of abnormal 99mTC-PYP and 201T1 myocardial scintigrams during myocardial infarction, 4) a better understanding of the role of cell swelling and its temporal relationship to the duration of myocardial ischemia, altered sodium, potassium ATPase myocardial tissue activity and its role in altering coronary blood flow, 5) the development of methods to measure localized ventricular wall motion and thickness during myocardial ischemia which would serve as sensitive indicators of localized ventricular function, 6) an investigation of alterations in cardiac lysosomes that occur during hypoxia and ischemia, 7) the development of sensitive radioimmunoassays for cardiac myoglobin and for CPK-B isoenzyme, and 8) studies directed at defining the timing, location and severity of alterations in membrane integrity in myocardial cells and subcellular structures during myocardial ischemia.